The present invention relates to direction control in well drilling and, more specifically to bottom hole assemblies for performing such drilling.
In the drilling industry there is a need to be able to directionally drill a well so that the well trajectory follows a desired path. This may be necessary in order to avoid another obstacle such as another well or in order to accurately aim for a reservoir to be exploited. One of the existing methods of doing this is to use a bottom hole assembly including an orienting device to steer the drill bit in the desired direction. One particular application for this equipment is in short radius gas wells which are drilled in an underbalanced condition (i.e. well flowing). This technique can significantly improve well productivity, and therefore well economics.
This type of well and operation has various specific characteristics. One is build-up rates of over 50xc2x0/100 ft (a radius of curvature below 30 to 35 m). This causes high bending forces on the tool; the tools need to physically bend around the curve, because the geometry does not allow straight tools to pass. There is therefore a need for short, slim assemblies to help with rig-up and to negotiate the bend. There is also undamped vibration coming from the drill bit and motor, which adversely affects tool life and reliability. The techniques and requirements of this type of application are already known but all existing equipment suffers from reliability and usability problems, resulting from the way in which the tools are designed.
The general object of the present invention is to provide an improved bottom hole assembly.
According to the invention there is provided a bottom hole assembly for drilling a well, comprising a non-magnetic tubing, an orienter, a motor and bit fed with drilling fluid which passes through the non-magnetic tubing, and a sensor package contained within the non-magnetic tubing. The assembly has a drilling fluid flow tube passing through the non-magnetic tubing adjacent to the sensor package, and means for determining the relative position measurement between the non-magnetic tubing and the motor. The relative position measurement is the difference between the toolface values (orientations) of the non-magnetic tubing and the motor.
The orienter is preferably of annular form, with the flow tube passing axially through it to the motor.
The present device is suitable for use with coiled tubing and has specific advantages, in terms of reliability and operation, which make it particularly suited to harsh environments